The present invention relates to delivery apparatus with a thrust piston pump for discharging media, particularly liquids from a storage vessel or the like in the normal position and the opposite inverted position, whereby the pump thereof has a cylinder and, for defining a pump chamber, a manually displaceable piston unit therein, together with a discharge passage and suction ports for the normal and inverted positions, whereof the suction port for the normal position is provided with a valve arrangement in the manner of a check valve closing in the case of an over-pressure in the pump chamber and in the inverted position in the case of a vacuum in the pump chamber, said valve having two valve seats arranged in opposing manner, in each case for the engagement of a movable valve body, for example a ball.
An atomizer is known (German Patent No. 28 18 560), in which two separate suction valves with separate valve bodies are arranged in axial succession in the suction port. In the case of such delivery, discharging or dispensing apparatuses, one of the suction valves both in the normal position and in the inverted position is used for closing the suction port during the pump stroke, i.e. in the case of an overpressure in the pump chamber, while the other suction valve serves to close the suction passage only in the inverted position under the weight force acting on the associated valve body and during the return stroke of the pump piston, so that a vacuum builds up in the pump chamber and towards the end of the return stroke medium is only sucked in via a separate suction port provided exclusively for the inverted position. So as to ensure during the following pump stroke performed in the inverted position, that there is only a discharge of medium through the discharge passage and not back into the storage vessel, the valve body of the first-mentioned suction valve must be brought into the closing position by the flow of a partial quantity of the medium displaced from the pump chamber counter to its weight force. Independently of the flow direction in which the valve bodies of the two discharge valves are successively arranged, this process is disturbed by the second discharge valve due to the flow resistances emanating therefrom, so that a rapid or immediate transfer of the valve body of the first discharge valve into the closed position is prevented, which leads to variations regarding the medium quantity discharged during each pump stroke, i.e. to dosing inaccuracies. The arrangement of two separate valve bodies is complicated and takes up a large amount of additional space.